A DC motor works by converting electrical energy into mechanical energy. This is accomplished by passing current through a coil located in a magnetic field which results in a force or torque that moves the coil linearly along an axis or spins the coil if the coil is on a rotational axis. The simplest DC motor is a single coil apparatus and is driven by a single phase current.
FIG. 1 is an isometric view of a typical linear DC motor 100 with a conventional magnetic circuit arrangement. The DC motor 100 comprises two permanent movable magnetic tracks 102 and a single phase coil 104 located between the magnetic tracks 102. A power supply supplies current to the coil 104 through electrical connections 106. When a current passes through the coil 104 in the presence of a magnetic field generated by the magnetic tracks 102, a force or a torque will be generated. However, with this simple construction, it is not possible simultaneously to control both the driving force and the heat generated in the DC motor 100.
A DC motor is advantageous as compared to a multi-phase AC motor as the magnetic circuit of a DC motor is simpler and the optimal generation of a force or torque is not dependent on information regarding the motor position. This feature makes DC motors particularly suitable for applications where positional information on the DC motor is difficult to obtain. On the other hand, heat control in a DC motor will typically require an external heater for maintaining thermal stability of the motor, but such an external heater increases component count and the cost of the system.
It is therefore desirable to devise a DC motor with independent torque and thermal control without having additional components and increased costs.